Heat pipe fin stack with extruded base

ABSTRACT

A heat sink has a base plate to be clamped against a heat source and one or more heat pipes containing a phase change fluid. Each heat pipe has an elongated tubular evaporator fitted in a channel in the base plate, and a columnar condenser part perpendicular to the base plate forming a structural column for air heat exchange fins. The channel in the base plate is parallel to an edge. An additional channel or ridge is provided, also parallel to the edge, for receiving a clamp or spring clip to urge the base plate against the heat source. The base plate is inexpensively extruded with the parallel channels, ridges, etc., extending across the width of the base plate parallel to the edge. The heat sink has a minimum number of inexpensive parts yet is highly thermally efficient.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of U.S. Provisional PatentApplication Ser. No. 60/388,781, filed Jun. 14, 2002.

FIELD OF THE INVENTION

The invention relates to the structure of heat exchangers, and inparticular a heat dissipation tower arrangement or heat sink fortransferring heat energy collected at a conductive base in contact witha thermal source such as an integrated circuit package. The heat istransferred via heat pipes carrying a phase-change fluid, into a set offins in contact with the ambient air. The heat pipe tubes fit incomplementary channels in the base, which extend parallel to one anotherand parallel to an edge of the base. The tubes are diverted upwardly toserve as columnar supports of the fins. This structure is simple andinexpensive in that the base can be a cut section of an extruded form towhich the heat pipes and fins are simply assembled. Yet the structurehas a substantial heat dissipation capacity.

BACKGROUND OF THE INVENTION

Certain semiconductor devices in electrical and electronic circuits,such as large scale integrated circuits, voltage regulators, currentswitching devices, high current drivers and other similar devices,generate heat that is deleterious to their operation and must bedissipated. An individual semiconductor junction may be subject tothermal runaway current conduction leading to further heating anddamage. In large scale digital integrated circuits, operation at orabove the maximum rated temperature can result in spurious switchingoperations and functional failure.

In a highly integrated semiconductor device such as a computerprocessor, a single semiconductor switching transistor may conductlittle concurrent on its own, but is densely mounted with many othertransistors. A single integrated device

may generate heat energy of a hundred Watts or more. Supplementalcooling arrangements may be needed in addition to convective cooling byheat driven circulation of ambient air, conduction of heat throughcircuit lands and the like, for maintaining operational temperatureswithin design ranges. For this purpose, thermally conductive heat sinkdevices, normally of cast or sheet metal and having a substantialsurface area exposed to the air, are mounted on a base that is clampedto bear physically against the heat generating circuit element.

A large-scale integrated circuit such as a computer processor or similardevice typically is mounted removably in a receptacle that is solderedto a printed circuit board. The receptacle has inward-facing resilientcontacts for conductively coupling to contacts on the circuit package,which package may be several cm on a side. The receptacle or auxiliarystructures associated with the printed circuit board carry spring-clipclamping mechanisms that engage over part of the heat sink, rested atopthe circuit package. The clamping mechanism physically presses a heatsink against the circuit package when mounted. The heat sink typicallycomprises a base block that is relatively thick, integrally cast with anarray of thin fins functioning as a heat exchanger to release heat intothe ambient air. The array of fins and/or the base has structure tocooperate with the clamping mechanism, and can also provide a point ofattachment for a fan for forcing a flow of air over the fins.

Heat energy diffuses from the active circuit elements into the circuitsubstrate and into the circuit packaging structure, which comprisesthermally conductive plastic or ceramic. The heat energy diffuses byconductive contact into the base of the heat sink, and then diffusesthrough the integral or thermally conductively attached structures ofthe heat sink to the surfaces at which air contact heat exchangeconvection carries the heat away. The array of fins typically is castintegrally with the heat sink base, but also can be thermallyconductively attached in contact with the base. The function of the finsis to present a relatively large surface area, preferably within arelatively small total volume, for efficient thermal energy release. Theelectrically powered fan, mounted on the heat exchanger by screws orclamps, forces air over the heat exchanger fins and may improve thermaltransfer. However, the fan also dissipates a certain amount of heat intothe air. The heat sink spreads out the heat energy from the source,primarily the integrated circuit, into the cabinet or housing volume ofthe device. Another fan may be provided to circulate air between thehousing and the ambient room air.

Integrated circuit devices are available according to more or lessdemanding temperature specifications. Devices that have a relativelywider temperature range are more expensive. Standard commercial computerprocessor components, for example, may be rated up to 70° C. (about 160°F.). The most durable military application devices may be rated up 125°C. (about 260° F.). These devices are sometimes required to operate inambient air temperature conditions ranging from −40 to +55° C. (about−40 to +130° F.).

Movement of thermal energy from an integrated circuit or other localizedheat source, toward a remote area or toward a structure that carries theheat away, occurs from one or more of thermal conduction, convection andradiation. Conduction of heat energy requires contact between thermallyconductive masses and proceeds at a rate that depends in part on thedifference in temperature between the masses. Convection involvesconduction between a heated body and adjacent heat transfer fluid (gasor liquid), typically air, involves differences in fluid density due todifferences in fluid temperature, and is substantially affected byforced air currents. Radiation also dissipates heat, but itscontribution is normally small at the temperature ranges of interest.

Heat transfer arrangements can involve passing a current of cooler airor other heat transfer fluid over a hotter surface to be cooled. Acaptive heat transfer fluid can be provided in closed volume andarranged to circulate. The fluid is heated by a source of heat energythat is in heat transfer relationship with one part of the closedvolume. A heat sink is arranged in heat transfer relationship withanother part of the closed volume, releasing heat (provided that theheat exchange medium, such as air, is kept cooler than the heat sink),and cooling the fluid. The heat transfer fluid advantageously undergoescyclic changes of phase. Each change of phase either stores or releasesa quantity of heat energy due to the latent thermal energy involved inthe phase change itself.

In this way, a liquid phase change heat transfer fluid can be evaporated(vaporized) into gas at the heat source and condensed again into liquidat the heat sink. Different techniques can be used to return thecondensed liquid from the condenser to the evaporator, which need not bepowered by outside energy sources. A return path is possible, forexample, over a gravity flow path in a thermo-siphon arrangement. In aheat pipe arrangement, a return path for the condensed liquid can beprovided by lining the vessel confining the heat transfer fluid with awicking material that supports capillary flow, such as a sinteredparticulate or powder lining. The capillary flow is driven substantiallyby surface tension and can proceed regardless of orientation andgravity.

Assuming that the heat transfer fluid is confined in an integral metalvessel, some thermal conduction from the heat source to the sink canoccur through the vessel walls. It is desirable on grounds of efficiencyto separate the evaporator and condenser sections by a distance orotherwise to interpose a thermal barrier that permits maintenance of atemperature difference. Nevertheless, phase change heat exchangecircuits as described can operate with a very modest temperaturedifference between the source and the sink and can efficiently move heatenergy to assist in heat dissipation.

There are a number of design considerations for thermal transferarrangements such as heat pipes. In addition to the ability to handlethe necessary flow of thermal energy to keep the heat source withindesired temperature limits, the evaporator and the condenser should havea good heat transfer coupling with the heat source and sink,respectively. The thermal transfer characteristics of the heat pipestructures, the various dimensions and quantities, etc. need to operateover the range of expected temperatures. Preferably the device iscompact and does not interfere unduly with necessary access tostructures associated with the heat source and sink.

A number of heat pipe arrangements according to the foregoing generaldescription are available from Thermacore International, Inc.,Lancaster, Pa., and are disclosed in US patents assigned to theirlicensor, Thermal Corp., Georgetown, Del. In a heat pipe, the liquid andvapor phases of the heat transfer medium reach equilibrium in theabsence of temperature differences and remain substantially stagnant.When heat energy is added at the evaporator, a temperature differencearises. Vaporization of the heat transfer medium at the evaporator leadsto increased local vapor pressure in that area. The vapor diffusesthrough the envelope of the heat pipe, and a portion arrives at thecondenser. The condenser is at a slightly lower temperature. As thevapor is cooled and condenses, releasing the latent heat energy ofvaporization at the area of the condenser, heat energy is transferredfrom the heat transfer medium to the heat pipe envelope, where air heatexchange fins remove the heat energy.

The condensed liquid phase heat transfer medium flows back to theevaporator due to capillary forces developed in the wick structure, andthe cycle can repeat. Where there is a positive temperature differencebetween the evaporator (e.g., warmed by an electrical circuit element)and the condenser (e.g., cooled by convection, forced air, contact witha thermal sink, etc.) the cycle can continue indefinitely, moving heatenergy. The technique is operative at low thermal gradients. Theoperation is passive in that it can be driven wholly by the heat energythat it transfers.

U.S. Pat. Nos. 6,381,135—Prasher; 6,389,696—Heil; and6,382,309—Kroliczek teach additional heat dissipation apparatus intendedfor cooling integrated circuit devices and the like, as described. Thesereferences are hereby incorporated for their teachings of heat pipe orthermal siphon devices.

A stacked-fin heat sink device for a large scale integrated circuit orprocessor chip package is disclosed in U.S. Pat. No. 6,061,235—Cromwellet al. In that device, a mounting fixture is attached to the motherboardor other circuit card to surround the processor, and the fixturereceives a spring biased mounting that presses a thermally conductivebase plate into mechanical and thermally conductive contact with theprocessor package. A heat pipe is contained in a cylindrical vesseldisposed centrally on and longitudinally extending perpendicular to thethermally conductive plate. A plurality of heat transfer fins aredisposed parallel to one another and perpendicular to the extension ofthe cylindrical vessel. In this patent, which is hereby incorporated inthis disclosure, the thermally conductive plate at the bottom end of theheat pipe vessel can function as the evaporator, having a slightlyhigher temperature than the finned sidewalls of the vessel remote fromthe bottom, which maintain a lower temperature and can function as thecondenser. In the standing configuration shown, gravity can power thereturn path. In other orientations, a wicking material can be providedso that capillary action drives the return path.

The spaced air-contact fins in Cromwell need to be assembled with theheat pipe tube. Whereas the fins are rectangular and the heat pipe is acylinder, there are issues respecting vertical, horizontal androtational alignment of the plates to the one another, and attachment tothe cylinder in good thermally conductive contact. These problems appearto have been addressed by affixing the fins to opposed side plates, thusrequiring additional parts and assembly while affecting the extent ofavailable air circulation. Air circulation characteristics and heattransfer characteristics are also affected by the relative size of theheat pipe and the fins. It would be advantageous if the structure ofsuch a heat sink could be minimized, preferably such that the heat pipeprovide substantially all the structural support needed for the fins.

A mounting base plate arrangement has certain potentially useful aspectsin connection with a heat transfer device. A plate is useful to presenta large surface area for contact with a heat source having a planarsurface, such as a processor or VLSI circuit. The rate of heat transferby conduction is partly a function of the area and intimacy of contact.The plate can have a reasonably substantial thickness, which provides athermal storage capacity and leads to rapid heat transfer throughout thematerial of the plate. Apart from these benefits, the drawbacks includethe complications associated with mounting the plate to the heat source,and the need to mount the heat pipe vessel to the base plate and tomount the fins. These needs are met in part by providing structures onthe base plate. The structures can include a clasp part that iscomplementary with a spring clip for affixing the base plate to the heatsources. The structures can also include structures that arecomplementary with the external structure of the heat pipe vessel, whichis capable of various shapes. The structure of the base plate can evenprovide one or more walls that are assembled to close the heat pipevessel.

However there is a strong interest in controlling the complication andexpense of heat sinks. Heat sinks are preferably made in a manner thatmaximizes thermal efficiency by providing good contact between the heatsource, the heat pipe and the fins. The optimal structure should havevery inexpensive parts, mounted by very inexpensive assembly steps, butshould provide good thermal efficiency.

It would be advantageous to reduce the complexity of a heat sinkcontaining a heat pipe, to the minimum necessary to achieve theobjectives of efficient heat transfer and the structural connectionsthat are involved.

SUMMARY OF THE INVENTION

It is an object of the invention concurrently to improve ease ofmanufacture and to reduce the expense of a heat sink device, whileproviding good structural integrity and thermal energy transferefficiency.

It is an object to employ at least one and preferably a plurality ofheat pipe vessels as structural support elements that function to mountan air-exchange heat transfer fins on a source-contact heat transferbase.

It is another object to minimize the number and complexity of partsneeded to construct a heat dissipation device carried on a base platehaving structures for attachment to a heat source and for receiving aclamping fixture, and to enable the use of a base plated that requiresno supplemental drilling, bending or similar shaping steps.

It is still another object to provide a heat sink on a base plate thatis capable of certain variations in the respective location of itsparts.

These and other objects are met in a heat transfer device such as a heatsink, carried on a base plate having parallel depressions extendingacross the full extension of the base plate, for receiving heat pipetubes in thermal engagement with the base plate, and also for receivingspring clip clamping fixtures for attaching the base plate to a heatsource. The depressions for the heat pipe tubes are subject tovariations that are discussed herein. By providing mounting structureson the base plate that are substantially met by shaped grooves ordepressions extending across the base plate, the base plate can besimply extruded in its final shape, no machining or drilling steps beingrequired.

The heat pipe tubes have a working fluid in a vessel with a wickingmaterial between an evaporator and condenser. Preferably two paralleldual heat pipe tubes are provided, each having a U-shape wherein thebottom of the U-shape fits in a corresponding depression across the baseplate and the legs of the U-shape function as standing columns thatsupport air heat exchange fins.

According to the respective embodiments, the depressions for the heatpipes can be squared or rounded in cross section. The depressions forthe heat pipes and also the structures for the spring clips, canexclusively involve elongated channel shapes across the base plate, orcan include raised ridges.

The legs of one or more U-shaped tubular heat pipes form the structuralcolumns that carry a stack of air heat exchange fins. These legs can bespaced by a distance less than the extension of the base plate, suchthat the legs are bent upwardly from the channels formed in the baseplate. The legs alternatively can be spaced by a distance greater thanthe width of the base plate, such that the legs are bent upwardly at adistance on either side from the base plate. In this arrangement, thebottom of the U-shape of the heat pipe tubes can be on either side ofthe baseplate.

The device as thus configured is easily and inexpensively manufactured.The heat pipes can be charged and sealed before assembly or afterwards,because the ends of the U-shapes remain accessible. Although notexcluded, no supplemental fasteners are needed to arrange and supportthe assembled parts, all necessary structural interconnections beingenabled by the shape of the base plate and the associated heat pipe tubeand spring clips. The base plate can be shaped as a rectilinearmonolithic extrusion having parallel oriented channels on one or bothsides, which are cut or extruded, for receiving the bottoms of U-shapedheat pipe tubes. Preferably the spring clips or the like for attachingthe base plate to a computer processor or VLSI chip or other heat sourceengage with additional channels arranged to straddle the heap pipe tubechannels, although a raised ridge is also possible.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully disclosed in, or rendered obvious by, the following detaileddescription of the preferred embodiments of the invention, which are tobe considered together with the accompanying drawings wherein likenumbers refer to like parts and further wherein:

FIG. 1 is a perspective view of a heat dissipation tower or heat sinkfor circuit devices according to an embodiment of the invention havingtwo dual heat pipes.

FIG. 2 is a perspective view showing the base plate part of the deviceaccording to one embodiment

FIG. 3 is an exploded perspective view illustrating assembly of therespective parts.

FIG. 4 is a partially sectional elevation view showing the heat sinkdevice installed on a circuit element to be cooled.

FIGS. 5 through 8 are partially sectional elevation views illustratingcertain variations in the shape and placement of base plate channels andridges according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This description of preferred embodiments is intended to be read inconnection with the accompanying drawings, together forming thedescription of the invention and illustrating certain nonlimitingexamples. The drawing figures are not necessarily to scale and certainfeatures are represented in schematic form in the interest of clarityand conciseness.

Spatial and relative terms denoting an overall orientation, such as“horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well astheir derivatives (e.g., “horizontally,” “downwardly,” “upwardly,” etc.)are intended to refer to the orientation as then described or as shownin the drawing figure under discussion. These terms are used forconvenience of description and are not intended to require a particularorientation unless that is clear in the context.

Likewise, internally relative terms such as “inwardly” versus“outwardly,” “longitudinal” versus “lateral” and the like are to beinterpreted relative to one another or relative to an axis ofelongation, rotation, assembly or the like, as appropriate to thedescription.

Terms stating relationships of attachment, coupling and the like, suchas “connected” and “interconnected,” refer to a relationship wherein thestructures can be attached, coupled, connected (etc.) directly orindirectly through intervening structures. Such attachments, couplingsand the like can be movable or rigid attachments, unless the descriptionindicates otherwise. Where elements are “operatively” connected,attached, or coupled, that connection, attachment or coupling isintended to denote a connection or the like that allows the pertinentstructures to operate as stated, by virtue of such relationship.

Insofar as the description and claims recite means-plus-function clausesor elements are defined by their function, those elements are intendedto encompass the structures described, suggested, or obvious in view ofthe written description and/or drawings for performing the recitedfunction.

A heat transfer device or heat sink 20 as shown in FIG. 1 includes twodual condenser heat pipes 29 carried on a base plate 33. Each of theheat pipes 29 generally comprises a hollow tube forming a closedenvelope or volume in which a heat transfer fluid is disposed. The heatpipes preferably are lined with a wicking material that distributes theliquid phase of the heat transfer fluid within the envelope.

Each of the heat pipes 29, two being shown in FIG. 1, is generallyU-shaped. The standing legs 52 of each tube form structural columns thatsupport a stacked array of fins 44. The bottom portions 56 of theU-shape (see FIG. 3) are arranged to fit in elongated channels 42 inbase plate 33 that is, each of which is formed in a general U-shapehaving standing legs 52.

FIG. 2 shows the base plate 33 separately. The base plate 33 ispreferably a monolithic or integral slab of material with elongatedchannels 42 for affixing the heat pipes 29. The channels 42 in thisembodiment are parallel to the ends of the base plate 33 and spacedinwardly from the ends, this space being occupied by elongated ridges orchannels 46, which provide a point at which the base plate 33 can beengaged by a clamp or the like, discussed below with respect to FIG. 4.

In FIG. 2, it is shown that the channel and ridge configurations on baseplate 33 are all parallel. By virtue of this structure, base plate 33 isvery easily and inexpensively produced. Base plate 33 can be monolithicmetal, for example aluminum, or another material such as conductiveplastic, extruded in the direction of elongation of channels 42, 46 andsimply cut to length along a line perpendicular to the direction ofextrusion.

It is also possible to produce the base plate in other ways, for exampleby cutting the elongated channels and contours from a larger solid slab.However an important advantage of the structure as shown is that it canbe simply extruded at very minimal cost.

The heat sink device is assembled as shown in FIG. 3. The heat pipes 29are arranged such that the standing legs 52 of their U-shaped forms aredisposed perpendicular to the plane of the base plate 33. The bottomsegments 56 of the U-shaped heat pipes are fit into the elongatedchannels 42, which in the embodiment shown in FIG. 2 are on the upperfacing surface of the base plate 33.

The air heat exchange fins 44 are mounted over the standing column legs52 of the heat pipes 29. Preferably, the fins 44 are mounted by pressfitting the fins 44 at their holes 53, over the standing column parts 52of heat pipes 29. The respective parts can be permanently affixed, forexample, by soldering, adhesive or the like. Alternatively, the heatpipes 29 can be soldered or adhered to the base plate 33, leavingfreedom to displace the fins 44 on the column legs 52 of heat pipes 29,if necessary to provide clearance with some other part (not shown).

Referring to FIG. 4, in a preferred arrangement the fins 44 are arrangedwith openings 53 that are stamped or similarly formed to have a hub orcollar portion of the fin 44, extending for a short longitudinaldistance along the leg 52 of the heat pipe. This short collar improvesstructural rigidity of the stacked fins and also provides for goodthermally conductive contact between the standing leg 52 and the fin 44.

The bottom part 56 of the U-shaped heat pipe vessel 29 is placed inrelatively closer thermally conductive relation with the heat source 70(shown in FIG. 4), such as an integrated circuit, than are the standinglegs 52. Accordingly, the bottom part 56 of the U-shaped heat pipe 29becomes slightly warmer due to heating from the source 70 asconductively coupled to the bottom part 56 through base plate 33. Thebottom part 56 functions as an evaporator and vaporizes the liquid phaseof a heat transfer medium therein.

The vaporized medium diffuses through the envelope that includes bottompart 56 and standing legs 52. The standing legs are slightly cooler dueto dissipation of heat energy into fins 44 and by convection into theambient air. Therefore, the leg portions 52 function as condensers,where the heat transfer medium is condensed from the gaseous phase tothe liquid phase. With changes of phase from liquid to gas and from gasto liquid, the latent energy of vaporization is stored in the heattransfer medium. Due to this cyclic storage and release of latent heatenergy, the coolant carries substantially more heat energy from baseplate 33 and source 70 to the fins 44, than would be possible in thecase of flowing heat transfer medium that does not change phase. The gaspressure conditions in the heat pipe are established by partiallyevacuating the heat pipe when charging the heat pipe with liquid heattransfer medium. An equilibrium is established when the heat pipe isthen sealed. The charging and sealing can be accomplished by providing asmall passage at the top end of one of the standing columns 52, whichcan be pinched off or plugged with solder or adhesive after charging.

Referring to FIG. 4, the base plate 33 is clamped in direct thermallyconductive contact with the integrated circuit package 70 (or other heatsource to be cooled). For this purpose, a spring clip 62 or similarclamp mechanism is provided and is arranged to engage with acomplementary channel 46 on the base plate. The channel 46, like thechannel 42 for the bottom part of the heat pipe, is a fully elongatedchannel that can be formed during extrusion. Channel 46, like channel42, extends across the full width of the base plate 33.

The spring clip 62 or similar clamp mechanism can be attached inconventional manner to the circuit board (not shown), for example at asurface mounted receptacle for the integrated circuit package 70.Various forms of similar clamp mechanisms are possible, in the form ofbale clips, pivoting clasps and springs.

FIGS. 5-7 illustrate some alternative complementary arrangements for thecross sectional shape of the bottom part 56 of the heat pipe 29 and thechannel 42 in the base plate 33. These shapes each have benefits anddrawbacks. FIGS. 5-7 also show possible variations in the shape of thechannel or ridge 46 that is engaged by the clamping mechanism 62 (shownin FIG. 4).

In FIG. 7, the evaporator or bottom part 56 of the heat pipe has a roundcross section, the bottom part being a cylindrical hollow tubecontaining a heat transfer medium and being lined with a wickingmaterial (not shown in FIG. 7). A benefit of this arrangement is that upto the centerline of the heat pipe tube 56, the semi-cylindrical shapeof the channel 42 in the base plate 33 is fully complementary with theoutside shape of the heat pipe tube 56. This full surface contactprovides for good heat conduction from the base plate 33 to the heatpipe tube 56 and the heat transfer medium therein.

A drawback of the cylindrical shape in FIG. 7 is that there is sometendency for the heat pipe tube 56 to rotate prior to permanentaffixation. If the standing legs 52 of the heat pipe are permitted tobear against the lateral side of channel 42, the direct contact betweenthe bottom part 56 and the base plate may be lost. Therefore, some careis needed in aligning these parts properly.

In FIG. 6, the bottom face of the channel 42 in the base plate 33 isflat, and the bottom part 56 is D-shaped in cross section with the flatside on the bottom of the base plate channel 42. This arrangementprovides good surface contact over the area of flat bottom of thechannel 42, and also provides relatively positive alignment. However thearea of contact is somewhat less. In FIG. 6, like in FIGS. 5 and 7, theclamp-receiving structure is a channel 46, whereas in FIG. 8 thecorresponding structure is a ridge 47.

FIGS. 7 and 8 show that the manufacturing ease and very limited expenseaspects of the base plate 33 are also achieved if the bottom part of theU-shaped heat pipe resides below the base plate and thus in directcontact with the heat source 70 as in FIG. 4. The embodiment of FIG. 7is particularly efficient for thermal energy transfer. The flat D-shapedbottom of the bottom part 56 of the heat pipe is in direct contact withthe source and the rounded remaining walls of part 56 are in directcontact with the base plate 33. This provides even more intimatethermally conductive contact with the heat source and is relatively moreeasily aligned then the round contour in FIG. 5 because the flat bottomin FIG. 7 is aligned when flush with the underside of base plate 33.

FIG. 8 provides further alignment benefits in a lozenge-shaped crosssectional evaporator as the bottom part 56 of a U-shaped heat pipe. Thisstructure provides reasonably full surface contact together withpositive positioning because the opposite sides of the lozenge shapedbottom part 56 are parallel and are pressed into contact with the baseplate and the heat source on opposite sides.

The ridge 47 for engaging with the spring clip or clamp 62 (see alsoFIG. 4) functions in the same way as the channel shaped version 46 inFIGS. 5-7. The spring clip or clamp has a portion that engages over andlaterally beyond an edge formed by the side wall of channel 46 or ridge47 to clamp the base plate in place.

In each of the embodiments, the heat pipe can be press fit intoreceptacle channel 42 in the base plate 33. A solder or thermallyconductive resin or potting formulation can fill any spaces between thematerial of the base plate and that of the heat pipe. The bottom sidesof the base plate 33 and the facing surfaces of the bottom part 56 ofthe heat pipe, particularly in the arrangements where a flat surface isflush and exposed for contact with the heat source, the respectivesurface can be treated to enhance thermal conductivity. For example, theflat surfaces of the evaporator part 56 can be fly-cut so as to be flatand smooth, for example to a local dimensional tolerance of 0.001″, andthus complement a flat and incompressible circuit package surface.Alternatively, if the circuit passage is compressible, the evaporatorsurface can be roughened or patterned to increase the surface area ofcontact.

In the embodiments of FIGS. 1 and 3, the standing legs 52 of each heatpipe are spaced by less than the corresponding dimension of the baseplate 33. This arrangement is generally compact because the standinglegs are advantageously spaced from the edges of the fins 44, and thefins can be the same width and length as the base plate, forming acompact shape. In the embodiments of FIGS. 7 and 8, the standing legs 52are spaced more widely than the base plate and straddle the base plate.The base plate in that case is narrower than the fins, assuming that thestanding legs 52 are straight and aligned normal to the plane of thebase plate 33. However it is also possible to provide other shapesbesides the strictly squared U-shape with perpendicular bottom and sideparts 56, 52, for example having additional bends or inclined parts.

For best thermal efficiency, the contact between all heat transfersurfaces along the path of transfer of heat energy is as intimate asreasonably possible. In addition to maximizing contact area, the wall ofthe heat pipe should be thin and constructed of a thermally conductivemetal or like material.

An advantage of the invention is that in addition to functioning asstructural columns, the use of several heat pipes of relatively smallerdiameter produces greater surface area per unit volume than a singlelarger diameter structure (or perhaps a smaller number, such as twocolumns instead of four. As a result, there is a comparable heattransfer efficiency achieved in a smaller heat pipe volume.

An important advantage of the invention is that the parts are few, veryinexpensive and inexpensively assembled. Particularly in thearrangements with the evaporator tube exposed for contact, the thermalenergy transfer efficiency is very good. These advantages, includingminimized expense and maximized thermal efficiency, can be achieved in arange of structures having the attributes discussed herein. Instead ofhaving two dual heat pipes, it is possible to have more or fewer. Theindividual heat pipes need not be U-shaped. For example the heat pipescould be L-shaped, with a bottom length received in the base plate and asingle column at one side. Other arrangements with round or non-roundcross sections (e.g., polygonal cross sections) can be used. The tubescan be snap-fitted into the base plate by using suitable dimensionalrelationships.

The materials and other internal arrangements of the heat pipe canotherwise incorporate a number of the aspects of known heat pipes. Theheat pipe vessel(s) form an envelope containing a working fluid, andcould be oriented for gravity return of condensed fluid to theevaporator, but preferably have a wicking material along the insidewalls so as to return the condensed fluid by capillary action withoutregard to orientation. The wick can be structured as sintered particles,fibers or the like, adhered to the inside surfaces of the walls of thevessel. The vessel is vacuum tight and may be formed from a sealed tubeof thermally conductive material, e.g., aluminum, copper, titaniumalloy, tungsten, etc. Although shown as substantially tubular or tubularwith flattened surfaces for contact with the heat source, the heat pipevessels can take other shapes.

The working thermal transfer fluid can be selected from a variety ofwell known two phase fluids depending upon expected operationalconditions such as the operating temperature range over which the heattransfer device will operate. Appropriate fluids may include, forexample, one or more of water, Freon, ammonia, acetone, methanol,ethanol and the like. The prime requirements for a suitable workingfluid are compatibility with the materials forming wick and the envelopewall, good thermal stability, ease of wetting of the wick and wallmaterials as well as viscosity and surface tension attributes suitablefor capillary flow.

The working fluid can be charged into the heat pipe vessels before orafter the assembly with the base plate and heat transfer fins, becausethe arrangement is characterized by access to the heat pipe vessel afterassembly, at least at an end located at the uppermost fin. In that case,the vessel is first shaped and attached, but is unsealed at a limitedventing point for charging. The working fluid is added, e.g., afterpartially evacuating the air in the vessel. The charging passage isplugged by adhesive, soldering and/or crimping operations.

The pressure and working fluid charge are arranged to obtain anoperating vapor pressure in the vessel over the working temperaturerange, within vapor pressure limits that permit evaporation andcondensation to occur at different points in the vessel (i.e., at theevaporator and condenser parts) when maintained at design temperaturedifferences. For optimal results, at all points within the temperaturerange, the working fluid has advantageous characteristics including highlatent heat storage capacity, high thermal conductivity, low liquid andvapor viscosities, high surface tension and an acceptable freezing orpour point. Preferably, the quantity of working fluid in the vessel isat least enough to saturate any wick material provided, or to support agravity flow in a circulating manner in the absence of a wick.

In a preferred arrangement, the heat pipe vessel comprises one or moremetals such as silver, gold, copper, aluminum, titanium or their alloys.Polymeric materials are also useful, including materials known in theelectronics industry for heat transfer applications, such asthermoplastics (crystalline or non-crystalline, cross-linked ornon-cross-linked), thermosetting resins, elastomers or blends orcomposites thereof. Some illustrative examples of useful thermoplasticpolymers include, without limitation, polyolefins, such as polyethyleneor polypropylene, copolymers (including terpolymers, etc.) of olefinssuch as ethylene and propylene, with each other and with other monomerssuch as vinyl esters, acids or esters of unsaturated organic acids ormixtures thereof, halogenated vinyl or vinylidene polymers such aspolyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride,polyvinylidene fluoride and copolymers of these monomers with each otheror with other unsaturated monomers, polyesters, such aspoly(hexamethylene adipate or sebacate), poly(ethylene terephthalate)and poly(tetramethylene terephthalate), polyamides such as Nylon-6,Nylon-6,6, Nylon-6,10, Versamids, polystyrene, polyacrylonitrile,thermoplastic silicone resins, thermoplastic polyethers, thermoplasticmodified cellulose, polysulphones and the like.

Examples of some useful elastomeric resins for potting and adhesiveaspects include, without limitation, elastomeric gums and thermoplasticelastomers, natural or synthetic. The term “elastomeric gum”, refers topolymers which are noncrystalline and which exhibit after cross-linkingrubbery or elastomeric characteristics. The term “thermoplasticelastomer” refers to materials which exhibit, in various temperatureranges, at least some elastomer properties. Such materials generallycontain thermoplastic and elastomeric moieties. For purposes of thisinvention, the elastomer resin can be cross-linked or not cross-linkedwhen used in the inventive compositions.

Illustrative examples of some suitable elastomeric gums for use in thisinvention include, without limitation, polyisoprene (both natural andsynthetic), ethylene-propylene random copolymers, poly(isobutylene),styrene-butadiene random copolymer rubbers,styrene-acrylonitrile-butadiene terpolymer rubbers with and withoutadded copolymerized amounts of unsaturated carboxylic acids,polyacrylate rubbers, polyurethane gums, random copolymers of vinylidenefluoride and, for example, hexafluoropropylene, polychloroprene,chlorinated polyethylene, chlorosulphonated polyethylene, polyethers,plasticized poly(vinyl chloride), substantially non-crystalline randomco- or ter-polymers of ethylene with vinyl esters or acids and esters ofunsaturated acids, silicone gums and base polymers, for example,poly(dimethyl siloxane), poly(methylphenyl siloxane) and poly(dimethylvinyl siloxanes).

Some illustrative examples of thermoplastic elastomers suitable for usein the invention include, without limitation, graft and blockcopolymers, such as random copolymers of ethylene and propylene graftedwith polyethylene or polypropylene side chains, and block copolymers of-olefins such as polyethylene or polypropylene with ethylene/propyleneor ethylene/propylene/diene rubbers, polystyrene with polybutadiene,polystyrene with polyisoprene, polystyrene with ethylene-propylenerubber, poly(vinylcyclohexane) with ethylene-propylene rubber,poly(-methylstyrene) with polysiloxanes, polycarbonates withpolysiloxanes, poly(tetramethylene terephthalate) withpoly(tetramethylene oxide) and thermoplastic polyurethane rubbers.

Examples of some thermosetting resins useful herein include, withoutlimitation, epoxy resins, such as resins made from epichlorohydrin andbisphenol A or epichlorohydrin and aliphatic polyols, such as glycerol,and which can be conventionally cured using amine or amide curingagents. Other examples include phenolic resins obtained by condensing aphenol with an aldehyde, e.g., phenol-formaldehyde resin. Otheradditives can also be present in the composition, including for examplefillers, pigments, antioxidants, fire retardants, cross-linking agents,adjuvants and the like.

It is to be understood that the invention is not limited only to theparticular constructions herein disclosed and shown in the drawings, butalso encompasses modifications or equivalents within the scope of theappended claims.

1-20. (canceled)
 21. A method for manufacturing a heat transfer devicecomprising: (A) providing at least one heat pipe having a flattenedevaporator part and a plurality of condenser parts that comprise anintegral extension of said evaporator part; (B) providing a base platedefining a channel extending across a full length of a surface of saidbase plate; and (C) fitting said flattened evaporator part in saidchannel.
 22. The method according to 21 wherein air heat exchangestructures are attached to at least one of said condenser parts.
 23. Themethod according to 22 including arranging said channel so as to beparallel to an edge of said base plate.
 24. The method according to 23further providing one of a channel and a ridge parallel to said edge, inaddition to said channel extending across a full length of a surface ofsaid base plate, for engaging a clamp for holding said base plateagainst a heat source.